The visual aspect of a liquid and particularly for beer represents a key element for most consumers. In that sense, the “brilliance” and the visual perception of beer's physical stability is an important quality aspect. The brewers carry out a series of distinct processing steps, each of which impacts on the final character and quality of the resulting beer product—including, for example, product clarity, and in particular beer “haze”.
Haze is a visual manifestation of the physical instability of the beer, and can be subdivided into three main groups, biological, microbial and non-biological. Biological hazes are caused by the presence of carbohydrate (e.g. unmodified starch, dextrin), beta-glucan, pentosan, and/or oxalate resulting from inappropriate processing steps. Microbial hazes, which cannot be remedied, are caused by infection of the beer by yeast, bacteria, mould or algae, and result from poor hygiene of the beer. Non-biological hazes, which are also characterized as colloidal hazes, are by far the largest clarity risk in beer, and this patent specification will principally focus on them.
The precursors responsible for the non-biological instability are proteins and polyphenols, and more specifically tannins. The formation of their complexes is increasingly exacerbated by parameters such as concentration of precursors, heat, oxygen, heavy metals, aldehydes and movement. It is also possible to make the distinction between “chill haze” and “permanent haze”.
“Chill haze” is formed when beer is chilled to 0° C. and re-dissolves when beer is warmed up to 20° C. or room temperature. It is a reversible complex formed by low molecular weight polyphenols and proteins, in which the hydrogen bonds are weak. The particle complexes are sub-micron sized (<1 μm), and can be considered as a precursor of the “permanent haze”.
“Permanent haze” is present in beer even at 20° C. and does not re-dissolve with time. This non-reversible haze is characterised by strong links, such as covalent bonds, between polymerised polyphenols and proteins. The complex size is up to 5 μm.
Haze intensity is defined by an EBC method (Analytica-EBC, Method 9.29, 5th edition 1997), which involves the measurement of light scattering at an angle of 90° to the incidence beam, calibrated with formazin standard solution. On the EBC scale, which is linear, the haze intensity of the beer is classified as follows:
Brilliant<0.5 EBCAlmost brilliant:0.5-1.0 EBCVery slightly hazy:1.0-2.0 EBCSlightly hazy:2.0-4.0 EBCHazy:4.0-8.0 EBCVery hazy>8.0 EBC
Certain studies show that the size of the particles contained in the haze could be characterized by using different scattering angles of measurement. It is generally recognized that 90° scattering angle is more sensitive to small particles, peaking around 0.5 μm, and is sensitive to particles so fine that the effect is difficultly perceived by human eye. The so called “90° haze” is also termed by some authors “invisible haze”. On the other hand, the 25° scattering angle does not suffer from the same visual effect and is more sensitive to larger particles, which are bigger than 0.5 μm. The so called “25° haze” is also termed by some authors “visible haze”.
There exists other unit scales with good correlation with the EBC scale:                NTU (Nephelomotric Turbidity Unit), where 4 NTU are equivalent to 1 EBC        ASBC (American Society of Brewing Chemists), where 69 ASBC are equivalent to 1 EBC.        
The major components of haze in beer are principally proteins and polyphenols but also small amounts of metal ions, oxalic acid, and polysaccharides.
Proteinaceous substances provide the greater part of non-biological hazes. Acidic proteins (esp. those having isoelectric point about pH 5.0) are important in the formation of chill haze and appear to be formed during mashing. Studies have shown that proline in haze-forming proteins is important for the interaction with polyphenols. These particular proteins derive mainly from malt hordein and are largely responsible for chill haze. As little as 2 mg/l of protein is enough to induce a beer haze of 1 EBC unit.
Tannins are important molecules in brewing and derive from, inter alias, both hops (20-30%) and malt (70-80%). They have the capacity to precipitate with proteins, which are denatured during wort boiling, to form the hot break and also in cold wort to form the cold break. During post fermentation process (e.g. cold storage), when the temperature is around 0° C., they are involved in the formation of chill haze and permanent hazes.
Polyphenols embrace a wide range of plant substances possessing in common an aromatic ring with one or more hydroxyl groups. Polyphenols may conveniently be divided into several classes, based on the chemical structure of the molecule:
                flavonols, monomeric species with structures of the type displayed by quercetin, but usually present in hops as glucosides,                    flavanols, monomeric species with structures of the type displayed by cathechin,            flavanoids, oligomers of flavanols (e.g. procyanidin B3, prodelphinidin B3),            proanthocyanidins, also called anthocyanogens, molecules cleavable by acid to form substance which polymerize in the presence of oxygen to pigments called anthocyanidins,            tannoids, polymers of flavanoids which are intermediates in the formation to tannins and,            tannins, polymers of flavanoids of a size sufficient to precipitate proteins.                        
Various studies have shown that monomeric polyphenols have little effect on haze formation but that dimers and trimers strongly accentuate haze formation. Polymerization of polyphenols is promoted by oxygen. The oxidation reaction can be catalysed by enzymes such as polyphenol oxidase and peroxidase.
Polyphenols on their own, contribute little to haze formation. Haze is instead composed fundamentally of complexes between condensed polyphenols (tannins) and proteins.
The mechanism of the interaction between sensitive proteins and polyphenols to create haze has been described by Chapon et al and is illustrate at FIG. 1.
Chapon's model states that in a complex matrix such as beer, proteins (P) and tannoids (T) are in chemical equilibrium in all steps of malt and beer production, with the protein/tannoid (P−T) product occurring in dissolved or insoluble form. The formation and the stability of P−T complexes are summarized as follows:P+TP−T→P−T (soluble) (soluble) (insoluble)
The soluble P−T is more likely in form of insoluble nanocolloids, much too small to lead to invisible haze. They serve however as nuclei for particle growth and subsequent haze development.
These chemical equilibria depend on the nature and structure of the tannoids and proteins. Moreover the probability for one sensitive protein to meet one tannoid depends on their relative concentration, the agitation and the temperature.
They can be shifted to the left, by removing either protein or tannoid, with less probable P-T precipitates.
As opposed to this, addition of high-molecular protein or tannin will shift equilibrium to the right, P−T compounds become insoluble and are precipitated. Cooling of beer has the same effect with P−T compounds becoming insoluble, due to increased interaction between P and T.
A third dimension can be added, which is time, during which, simple polyphenols (i.e. flavanols) polymerize to tannoids and then tannins. The polymerization rate is directly correlated to the initial concentration of polyphenols and the presence of oxygen.
There are a large numbers of factors that effect beer quality, and in particular its initial and long term haze.                Barley varieties vary considerably in their content of polyphenols. It is also recognized that maritime barley varieties are higher in polyphenols than continental varieties. The majority of the polyphenols are concentrated in the husk, and therefore winter barley has relatively higher levels compared to spring varieties. It is generally recognized that 6-row barleys have a higher level of polyphenols than 2-row barley varieties. Some low-anthocyanogen barley varieties have been developed and are used to improve the colloidal stability of beer. From the protein perspective, it is less clear that a given barley variety is particularly low or high in its level of haze-active protein, also called sensitive protein. It is reasonable to expect that a positive correlation exists between the potential haze formation and the level of nitrogen in the barley. The malting process can provide higher colloidal stability when the malt is well modified. The polyphenol level in raw materials impacts more on the future colloidal stability than protein level.        Replacement of barley with other sources of starch or carbohydrates (e.g. rice, maize, syrup) will dilute all types of haze precursors. Wheat based adjuncts on the other hand will increase risks in haze formation, due to the increased content of haze sensitive protein, polyphenol composition, presence of glucans and pentosans, if contains.        Hops also provide polyphenols, which are generally more polymerized as compared to the polyphenols which are present in malt. Aroma varieties tend to bring higher levels of polyphenols for an equivalent bitterness contribution.        
Malt grinding is the first operation, which can affect the colloidal stability, when oxygen is present together with polyphenols, resulting in a polymerisation and therefore increasing chill-haze precursors (e.g. potential precipitation of polyphenols with proteins).
Mashing involves mixing ground malt and other ground cereals with water in order to enzymatically degrade proteins into amino-acids and peptides and starch into fermentable sugars (e.g. glucose, maltose and maltotriose) and dextrins. The quality of the water plays an important role, and the brewer will preferably use water with a low residual alkalinity; low pH of the mash will promote enzymatic degradation of high molecular weight substances. High pH of water would increase the polyphenol extraction, with negative consequences on colloidal stability of beer. It is also important that there is sufficient calcium in the mash to ensure precipitation of oxalate. Methods of mashing affect the colloidal stability. For example decoction is better than infusion, because more protein denaturation, more polyphenol extraction and more oxidation, lead to better removal of haze precursor, via precipitation in the hot break and the cold break.                Filtration of the mash is a step which separates liquid and solid phases, where the liquid phase is called un-hopped wort. The pH of the sparging water is, as mentioned before, important for the colloidal stability. Moreover a high temperature and a high volume of water will extract more polyphenols. The polyphenol level, impacts negatively on the colloidal stability, if the polyphenols are not removed before bottling, and on the other hand impacts positively, if the they are removed (i.e. by precipitation), before bottling operation.        Wort boiling, in general, is to sterilize the wort, to remove the undesirable volatile compounds and to extract and isomerize the bitterness substance from hops, and to removed, by denaturation, excess of protein. This process step occurs during 60 and 90 minutes, and is essential for colloidal stability in order to obtain a well-formed hot break, which is the precipitable material that would otherwise survive the process to destabilize beer. The hot break is removed by decantation, centrifugation or by whirlpool. The intensity of the boil (evaporation of minimum 5-6% is required), the pH of wort (preferably between 5.1 and 5.3), agitation (as low as possible) and oxidation (negative for flavour stability, but positive for haze life due to the oxidation of polyphenols), are the most important parameters which influence the formation of hot break.        
Prior to the fermentation process the wort is cooled to fermentation temperature, oxygenated (either with air or pure oxygen) and pitched with yeast. Fermentation is the conversion by yeast of fermentable carbohydrates into ethanol, carbon dioxide and other compounds, which give the specific character of the beer. Depending on the yeast strain, the fermentation temperature ranges between 10° C. and 15° C. for lager yeast strains and between 20° C. and 30° C. for top fermentation yeast strains. During the fermentation stage, there is an adsorption of polyphenols onto the yeast cell surface. In the cold wort proteins, polyphenols and carbohydrates trend to interact with each other and to form sub-micron non-soluble particles, called “cold-break”. The resulting colloids can serve as nuclei for the further growth of chill-haze particle during cold maturation. The formation and the removal of the cold-break, and the association of tannins with proteins, both represent the major changes, impacting positively on the colloidal stability.
After the fermentation stage, beer is typically chilled to as low a temperature as possible without freezing (e.g. −2° C.). The cold-conditioning stage is particularly critical to develop “chill haze”. Each increase of the temperature will re-dissolve haze, and therefore will return haze precursors to beer, with the danger of developing the haze afterwards. At this stage, judicious use of finings can help the sedimentation of the formed haze.
Clarification is required following fermentation, because the beer is quite turbid due to the presence of yeast, protein/polyphenol complexes, and other insoluble material, all of which are responsible for haze formation in beer. Extended lagering periods at low temperatures, the addition of finings to the beer, and centrifugation are some of the techniques that brewers use to remove these substances.                The precipitable chill haze should be removed from beer, either during beer filtration or before. This operation can be realized by a simple elimination in whole or in part of at least part of the precipitated material, what brewers call “purge”, by transfer from tank to tank, and/or by centrifugation of beer.        Temperature control is critical, because their influence can re-dissolve quickly the haze precursors, with no possibility of re-precipitating the complex before the filtration step, with the consequence that the precursors will pass through the filter into the bright beer.        
The significance of a filtration operation in industrial processing derives not only from its direct impact on the filtered material, but also because it can be one of the last opportunities that a producer has to directly impact one or more of the quality determinants of the product. In the case of brewing, for example, filtration is typically the final pre-packaging step in the brewing process, and therefore perhaps the last chance that a brewer has to directly effect (in both the pro-active and the remedial sense) a beer's initial quality and, from a constituents perspective, its shelf-life.
As outlined by Gottkehaskamp, L., Oechsle, D., Precoat Filtration with Horizontal Filters, Brauwelt Int. 16, 128-131, 1998, the role of filtration in brewing includes improvements related to initial beer clarity, (as well as dealing in greater or lesser degree with incipient haze forming precursors), and factors that can adversely effect post-packaging flavour changes, primarily through: the removal of haze substances such as protein/polyphenol complexes, hop extracts and the like; aiding biological stability through the removal of at least a portion of the post-fermentation burden of micro-organisms; and removal of other dissolved macromolecules such as residual starches and dextrins as well as α- and β-glucans.
According to Donhauser, S., Wagner, D., Crossflow-Mikrofiltration von Hefe und Bier, Brauwelt 132, 1286-1300, 1992, kieselguhr alluviation has served for well over half a century as the dominant filter aid in beer filtration. Kieselguhr was first adopted in beer filtration in the United Kingdom in the late 1930's—but it was only later that it was actually adopted in the form in which it is currently most commonly used in the USA—and then subsequently introduced into the European brewing community.
While kieselguhr filtration (also known in the art as diatomaceous earths or “DE” filtration), is and may remain a major if not dominant type of filter aid mediated filtration (alluviation) for brewing and other industries (e.g. DE filtration is also employed in the wine making), there are a number of emergent, alternative filtration technologies. Technologies such as cross-flow micro filtration and a variety of membrane techniques have been introduced—although none have as yet gained widespread acceptance. (See for example, Meier, J., Modern Filtration—Overview of Technology and Processes, Brauwelt Int. 11, 443-447, 1993).
Filtration is generally understood in terms of a mechanical separation of various liquid/solid components from a suspended mixture thereof. These “suspensions”, (as used herein in the broad sense of the word, suspensions does not imply any particular particle size ranges, but only that the particulates are carried or suspended in the fluid flow), are passed through a porous filtration aid and at least some of the particulates are retained on or within the filtration medium while the then at least partially clarified liquid, (i.e. the “filtrate”), exits the filtration unit. Eβlinger, (Eβlinger, H. M., Die Bierfiltration, Brauwelt 132, 427-428, 1992), points out that there are a variety of distinctly different modes of the solid separation that employ filtration media:                surface or cake filtration, (sometimes also referred to as alluviation): wherein the solids in suspension together with an added amount of filter aid, (such as DE), are hold back by a filter cake supporting surface, on which the filter cake is built. Here, the solid separation takes only place at the surface of the cake;        deep or sheet filtration: The filter medium mostly consists of a thick layer with pores inside, which hold back the solid particles; and,        sieve filtration: Particles which are bigger than the filter pore size are kept on the surface of the medium.        
The application of the present invention and the particulars of its disclosure herein are primarily focused on the first of the above listed modes of filtration. In DE powder filtration (alluviation) the DE filter aid is injected into the beer stream at a location slightly upstream of the point where it is collected on a supporting mesh. Beer filtration is started when the precoats are established and the recirculating liquid is clear. The beer stream bearing the DE, together with the yeast and other suspended solids, then forms a largely “incompressible” mass referred to as the “filter-cake.” To prevent clogging of small pores of the filter and to achieve extended filter runs; the filter aid is continually metered into the unfiltered beer as “body feed.”
The porous bed supports a surface that traps suspended solids, removing them from the beer and the supporting bed is only “incompressible” in the sense that the beer can continue to pass through these pores as the filter cake continues to form and the operating pressures continue to rise over the course of the filter's operational cycle. For the purposes of mathematically modeling its flow-through characteristics, the cake is treated as being compressible—see the discussion below on porosity). The ongoing supply of filter aid, (referred to as “body-feed”), is continually added into the flow of beer to maintain the permeability of the cake. Not all of the particles will be trapped at the surface; some, and especially finer materials, will pass into the filter cake and be trapped—a process referred to as “depth filtration.” Depth filtration is not as effective as surface filtration, but is still a significant mechanism of filtration by filter aids. That inefficiency notwithstanding, it is prudent in all cases to start the body feed phase of the filtration cycle with a high dosing rate and decrease it as the differential pressure decreases across the filter bed. Under dosing of body feed will cause premature fouling of the surface of the filter cake, leading to an undesirably abbreviated filter cycle.
For alluviation filtration processes in general, (and including in particular those in which kieselguhr is employed as the filter aid), the common industrial filters can be classified by the following typology: 1) frame filters; 2) horizontal filters; and 3) candle filters.
Note in this connection that frame filters are what is referred to as “open”, and are not fully automated systems. Horizontal and candle filters, by comparison are “closed” and fully automated, (Kolcyk, M., Oechsle, D., Kesselfiltrationssysteme für die Anschwemmfiltration, Brauwelt 139, 294-298, 1999; and, Kolcyk, M., Vessel Filter Systems for Precoat Filtration, Brauwelt Int. 17, 225-229, 1999). The fact that frame filters are typically labor intensive with respect to cleaning, has lead to systems that are based on the other two filtration types gaining predominance in industrial applications. (See: Leeder, G., Comparing Kieselguhr Filter Technologies, Brew. Dist. Int. 21, 21-23, 1990).
In order to induce the suspension to flow efficiently through the filtration medium, (i.e. in order to compensate for the pressure drop in the fluid flow across the filtration medium, a pressure differential (usually by way of an upstream pump) in the operation of most filtration systems.
In the case of a hypothetical of “idealized” cake filtration with laminar flow through an incompressible porous filter cake by incompressible Newtonian fluids, Darcy's law is valid:dV/(A dt)=(u dP)/(ηL R)  {1}
Under these conditions, it follows that the specific flow u is proportional to the applied pressure difference dp and inversely proportional to the dynamic viscosity of the filtered liquid ηL. In other words, the higher the applied pressure difference and the lower the viscosity, the higher filtrate flow per surface unit (specific flow). In addition, the flow is also influenced by the filtration resistance R, which in turn depends on the flow resistance of both the cake and the filtration aid.
Eβlinger goes on to point out that in the more practical reality of a compressible filter cake, the specific gravity and therefore, the resistance of the filter cake is tremendously increased.
In addition, to the porosity of the filter cake, per se, the statistical distribution of the pore sizes plays an important role in filtration.
The Hagen-Poisseuille law describes the laminar flow through parallel cylindrical capillaries:dV/(dt A)=u=(dp εd02)/(ηL32 hk)  {2}with porosity ε, capillary diameter d0 and filter height hk.In reality however, the porosity function is validly described by the equation of Carman-Kozeny, which according to Eβlinger's detailed discussion, demonstrates that the influence of any given change in porosity, on the flow rate, is actually quite high. For example, if the porosity is decreased from 40 to 30%, the specific flow is reduced by 70%. The general differential equation for cake filtration is:dV/(dt A)=dP/(ηL(αhk +r0))  {3}with the specific cake resistance α and the resistance of the filter medium r0. In practical operations, almost all filter cakes are more or less compressible, especially those which originate from fine-grained and easily deformable solids.
For practical operations Darcy's law can also be written as (8):dp=u ηL hk/β  {4}with the cake permeability β
It follows from equation {4}, that an alluviation filter will behaves as follows: when the specific flow rate doubles, the pressure difference doubles accordingly. However, since dosage of body-feed must also be doubled in order to maintain the cake's permeability to enable flow, the cake depth doubles. Consequently, for a doubling of the specific flow rate, the pressure difference quadruples. However, to maintain the same pressure drop gradient through a filter run, when the specific flow rate is increased, the kieselguhr dose rate must be increased by the square of the new specific flow rate rationed to the original. Clearly, filter run time is inversely proportional to the quantity of kieselguhr dosed, (see for example, Leeder, G., The Performance of Kieselguhr Filtration—Can It be Improved?, Brew. Dist. Int. 23, 24-25, 1992.)
Alluviation filtration is further complicated by the available equipment options (see Leeder, G., Comparing Kieselguhr Filter Technologies, Brew. Dist. Int. 21, 21-23, 1990).
A horizontal filter (HF) consists of a one-piece vessel with two fixed horizontal metal plates. The element package consists of plate-like filter elements which are fixed to the central hollow shaft and are able to rotate due to a drive assembly. A leaf usually consists of a carrier plate supporting a strong coarse mash which, in turn, supports a fine mesh of openings of, for example only), about 70 μm. These items are bolted between peripheral clamps.
Unfiltered beer can enter the horizontal filter in two different ways depending on whether the particular horizontal filter is of the older S type or the more recent Z type.
The older construction allows the inlet to enter from the top metal plate and a distribution system (S-type). The beer-kieselguhr mixture is distributed from there between the vessel wall and the filter elements along the whole height of the filter. The filtrate is collected inside each filter plate and discharged via the hollow shaft. The S-type horizontal filter is characterized, (for example only), by a kieselguhr capacity of c. 7 kg/m2 and a max. operation pressure of 7 bar.
The more recent Z-type horizontal filter was developed in order to achieve a more even distribution of the unfiltered beer, by providing an individual filter feed supply to each filter element with an inlet distributor manifold. As a consequence of this inlet arrangement, the distances over which the beer flows are significantly reduced. Even in the case of Z-type horizontal filter filters equipped with large leaf diameters, the maximum flow distance is below 75 cm. This construction enables an even distribution of the filter aid on the leaf and therefore, promotes a relatively more homogenous filter cake of more uniform height. Gottkehaskamp et al, (supra), found in trials a mean cake height of 12 mm with a standard deviation of 0.8 mm for more than 700 points of reference.
The short flow distances in Z-type horizontal filter filters mitigate against redistribution of the filter aid in the unfiltered beer on the upstream side of the filter support or leaf. Since the resulting filter cake is therefore very (relatively speaking) uniform throughout the filter, the quality of the filtrates are much better and the pre-coat quantity can be reduced to a minimum. Furthermore, the space between any two adjacent filter elements can then be much more fully utilized, which in turn allows for larger volumes of beer to be produced in any given operational cycle. Such “longer operational cycles” lead in turn to a more economic filtration operation.
It is implicit from the overall design of a Z-type horizontal filter, that damage of the filter elements by a kieselguhr overload of the filter is unlikely. For example, a filter load up to 11 kg/m2 has been reported as being possible—and to cope with such high loading potential the Z-type horizontal filter is also designed for operating pressures of, for example, 9 bar. The benefit of operating at such pressures includes the fact that there is no reported negative impact on the quality of filtrate, (again, see Gottkehaskamp et al,—supra).
A typical candle filter consists of a cylindroconical vessel, which is separated in filtrate and retentate area by a plate. Another plate above this separation plate is used for filtrate collection. The cylindrical part of the vessel encloses the retentate area, while the conical part ensures a proper distribution of the raw kieselguhr and collects and discharges the waste kieselguhr at the end of filtration procedure. The non-filtered beer enters the vessel from the bottom tip of the conical part. The cylindrical candles are mounted vertically to the middle plate. They occupy around 55-75% of the vessel volume. A modern candle comprises a trapezoidal spiral wire welded, eight times per revolution, to rectangular support bars. The candle opening is asymmetric in that, externally it is 70 μm while internally, it is somewhat larger, thus avoiding the risk of plugging.
The surface per filter element is around 0.1-0.2 m2. In order to achieve a big filtration surface, many hundreds of candles have to be installed (e.g. 500 candles for a surface of 100 m2). candle filter can accept trub in an amount of c. 7 kg kieselguhr/m2. The candle filter construction is often designed for an operation pressure of max. 7 bar. Since there are no moving parts in a candle filter, it is called a static filter system.
Both, horizontal filter and candle filter are vessel filter systems, which show similarities. However, there are some decisive differences which are described as follows:
With respect to stability of filter cake, the horizontal filter provides a horizontal filter cake which is stable due to gravitation. Therefore, ongoing filtration is not affected by the stoppage of the plant, because the filter cake can not fall off the plate. In candle filter filtration however, the vertical filter cake has to be stabilized by a pressure difference caused by pumping. A shut down of the pump would result in slipping-off of the cake.
In connection with the pre-coating operation, a candle filter should be prepared by pre-coating immediately prior to the initiation of a filtration cycle. Otherwise the filter must be kept in the cycle modus which costs energy. Dealing with horizontal filtration, the filter preparation can be done already the day before filtration since the pre-coat is stable even without cycling and the filtration can be started at any time when the pre-coating is finished.
It is generally recognized for beer that the presence of yeast is limited to one yeast per liter, and the haze, is limited to 0.5 EBC with a maximum of 0.8 EBC (see paragraph on haze measurement), depending on beer specifications. DE can and is useful in delivering to these kinds of end product specifications. However, there are three fundamental problems inherent in the use of DE. First of all, DE affects the quality of the beer as it is a porous particulate, which leads to beer oxygen pick-up.
It also naturally contains slight amounts of metal ions which are catalysts for oxidation reactions. In addition, this material presents some health risks during its manipulation (e.g. inhalation). More recently these disadvantages have been compounded by the growing problem of disposal of the spent filter aids—and the associated costs thereof of waste disposal.
In the Practical Brewer, 1993, Master Brewers Association of America, point out that reactions leading to the formation of insolubles can continue even after filtration—and to deal with that problem, a variety of stabilization treatments can be employed. The effectiveness of DE filtration notwithstanding, there is often, although not always and in any case to varying degrees, an additional need to further enhance the colloidal stability of the beer. Essentially there are several candidate strategies for increasing the colloidal stability of beers: remove polyphenols, remove proteins, or remove a portion of each. Low temperature and low oxygen level are a pre-requisite for good general brewing practices in colloidal stabilization (and oxygen pick-up from DE can be a contributing problem in this connection too).                The removal of polyphenols is possible by adsorption on polyvinylpolypyrrolidone (PVPP), (or by precipitation with formaldehyde, which is for food-safety issues not generally a permitted practice). Due to its chemical structure, PVPP reacts preferably with polymerised polyphenols, flavanoids and tannins through hydrogen bonds and electrostatic weak forces. The affinity of polyphenols towards PVPP is higher than towards haze-active proteins in beer, due to the fact that PVPP has more active sites than proteins. Moreover, the interaction between polyphenols and PVPP is stronger and faster than between polyphenols and proteins. PVPP exists in two forms, the single use, which is finer (i.e. is a population made up of on balance, smaller particles) than the regenerable form. Single use PVPP presents a high surface/weight ratio, is dosed prior to the filtration, at a typical dosage rate between 10 and 30 g/hl, and is removed during the filtration step to make-up part of the filter cake. Regenerable PVPP is typically dosed continuously into the bright beer stream, between 25 and maximum 50 g/hl, and is collected on a specific filter (i.e. separate and apart from DE filtration), where it can be regenerated by contact with a solution of sodium hydroxide. This is the most economical way of producing a stable beer according to a shelf-life up to 6 months.        The removal of proteins is possible by adsorption on silica gels, silica sol or bentonite, by precipitation with gallotannins, or by enzymatic hydrolysis. Silica gel adsorbs proteins into its surface and the performance is a function of pore dimension, particle size, surface area and permeability. Silica gel removes preferably haze-forming protein, because it recognizes and interacts with the same sites on haze-active proteins as do polyphenols. Silica gels exist in three solid forms, the hydrogel, based on ≈70% moisture, the xerogel based on ≈5% moisture and the modified hydrogel, based on ≈30-35% moisture. The silica gel dosage can be applied during the cold maturation at a rate up to 50 g/hl, or in-line before the filtration step at a rate between 20 and 100 g/hl. A higher dosage rate could adversely affect the foam stability. Silica exists also on a liquid form, which is a colloidal silica hereafter called silica sol, to make the difference with silica gel, which is a powder. Due to its large surface area, the silica sol presents a high efficiency as adsorbing agent for haze-active proteins. Silica sol acts as silica gel acts, and the particles have the ability to cross-link and to form hydrogels with haze-active proteins, upon which they flocculate, finally forming sediment. Silica sol can be incorporated into wort or into beer. The addition to the hot wort is done at a rate between 40 and 70 g/hl of wort. When silica sol is added to the beer, the sol is injected directly into the beer stream during the transfer from fermentation to maturation at a rate of about 40 g/hl of beer, or the sol is injected directly into the beer stream during the transfer from maturation to filtration at a rate of about 15 g/hl of beer. Bentonite earth has long been used in the brewing industry, but is now rarely used, due to its non-specific binding with proteins, removing both haze and foam proteins. Gallotannins are naturally present in plants and can be extracted from gall nuts or Sumac leaves. It consists of polymerized tannic acid, which possesses many active sites (e.g. hydroxyl group) that react with protein in a similar way as tannoids, which explain the relative specificity for haze-active proteins. The insoluble complexes, which are formed can easily precipitate and can be removed from the beer. Tannic acid is not detrimental to foam stability when it is used at recommended dosage rates. Tannic acids exist in different commercial forms based on the product purity, and therefore may be used at different process steps: during wort boiling (2-6 g/hl), in cold beer maturation (5-7 g/hl), or just before the beer filtration (2-4 g/hl). The reaction time is relatively rapid and tannic acid may be dosed on-line, just prior to the beer filter. Due to the formation of a precipitate, the permeability of the filter cake will decrease, and it is recommended to use coarser grade of DE or a mix with perlite, in order to maintain the same filterability. Proteolytic enzymes hydrolyse hydrophobic proteins with no specificity for haze-active proteins, and consequently impact negatively on foam stability.        Various antioxidants (ascorbic acid and/or sulphites) have been used to either remove oxygen from beer or to negate its effect. These products may be added on-line during the filtration process, with a positive impact on colloidal stability.        
Given the aforementioned and growing problems associated with the use of DE, a number of attempts have been made to utilize alternative alluviation filter aids—and in particular, to produce synthetic materials that might serve instead of DE. Some of these are also regenerable. Particularly promising advances are described in detail in EP 91870168.1; WO 1996/35497; and, WO96/17923. However, in spite of the quality of these advances, they are limited in their ability to match DE performance, and hence have not been widely adopted. Notable in this connection is the difficulty in reproducibly matching synthetic filter aid cake porosity to that of DE—although there are other underlying considerations which also bear on the relative performance issue.
Accordingly, there remains a need in the art for improvements in and to synthetic alluviation filter aids and/or their application, that can be then adopted as effective alternatives to DE.